Features

This is a projection onto a cylinder tangent at the central
meridian. Distortion of both shape and area are functions of distance
from the central meridian. Scale is true along the central meridian
and along any straight line perpendicular to the central meridian
(i.e., it is equidistant).

Parallels

For cylindrical projections, only one standard parallel is specified.
The other standard parallel is the same latitude with the opposite
sign. For this projection, the standard parallel of the
base projection is by definition fixed at 0º.

Remarks

This projection is the transverse aspect of the Plate Carrée
projection, developed by César François Cassini de Thury
(1714–1784). It is still used for the topographic mapping of
a few countries.

cassinistd implements the Cassini projection
directly on a sphere or reference ellipsoid, as opposed to using
the equidistant cylindrical projection in transverse mode as in function cassini.
Distinct forms are used for the sphere and ellipsoid, because approximations
in the ellipsoidal formulation cause it to be appropriate only within
a zone that extends 3 or 4 degrees in longitude on either side of
the central meridian.